Appraisal of the overburden mass and boundary conditions on the rocking behaviour of the vertical spanning strip wall

Abstract

Unreinforced masonry structures are particularly vulnerable to seismic events. Specifically, local out-of-plane mechanisms form recurrently, posing a serious threat of collapse. Among them, a Vertical Spanning Strip Wall (VSSW) mechanism occurs when a portion of a wall is solely constrained at its top and base, experiencing out-of-plane bending across its height. During the formation of the mechanism and up to collapse, the VSSW presents a highly nonlinear dynamic behaviour governed by the presence of an overlying wall or diaphragm and a diversity of diaphragm-to-wall connections. The present work simulates the dynamics of a VSSW, accounting for the influence of the overburden mass and a variety of boundary conditions through a two-rigid-body single-degree-of-freedom model. In addition, this study examines the energy losses of the VSSW and provides closed-form expressions to estimate the angular coefficient of restitution either analytically for predictive purposes or experimentally for characterisation campaigns. Finally, a series of illustrative comparative free- and forced-rocking analyses highlight the importance of the overburden mass and boundary conditions on the dynamic stability of the VSSW.